1. Technical Field
The invention relates generally to illumination devices, and more specifically, to an illumination device that includes one or more electromagnetic radiation sources that are adjustable based on a measured characteristic of an illuminated object.
2. Related Art
In illumination devices, two important characteristics are the efficiency with which it can generate electromagnetic radiation (e.g., radiant efficiency), and the efficacy of the generated electromagnetic radiation. In general, the radiant efficiency depends on the device power conversion performance, and has typically improved as technology matures. For example, to improve the radiant efficiency of an illumination device such as a light emitting diode (LED), one can seek to maximize both its internal quantum efficiency and its light extraction efficiency.
An acceptable efficacy of the electromagnetic radiation may be application dependent and/or based on one or more characteristics of an object being illuminated. In general, the efficacy of white light for a lighting application can be measured by its color rendering index (CRI). The CRI provides a quantitative measurement of how well the light renders objects of various colors. Based on the application, different values may be acceptable. Another measurement of the efficacy of white light is its spectral power distribution (SPD). The SPD measurement analyzes the relative power contributions from the various electromagnetic wavelengths that are combined to produce the electromagnetic radiation, e.g., the white light. In general, one can optimize the SPD of white light in order to obtain a higher CRI. In order to maintain white light having a desired SPD and/or CRI, several solutions incorporate feedback of the generated light.
However, the optimum SPD may vary based on one or more characteristics of the illuminated object(s). For example, an automobile headlamp should provide a very bright illumination of the road, while not blinding or creating excessive glare for the oncoming traffic. However, to date, no solution has been proposed that adjusts the SPD of electromagnetic radiation based on a characteristic of an illuminated object.
As a result, a need exists for a device that generates electromagnetic radiation that can be adjusted based on an illuminated object. In particular, a need exists a method and system for generating electromagnetic radiation that adjusts the electromagnetic radiation based on a measured characteristic of an illuminated object.